We recently got an interesting email from Lonely Planet, the folks who put out off-the-beaten-path guidebooks.

They had compiled a list of 20 classic regional sandwiches in honor of National Sandwich Month, which we’re in. (You can check out the full list by clicking here.) You’re probably familiar with many of their choices: muffulettas and po’boys from New Orleans, lobster rolls from New England, Italian beef from Chicago. Others we had heard of but not encountered (Louisville, Ky.’s “hot brown”) or hadn’t heard of period (the “Horseshoe” from Springfield, Ill. and environs.

There was one more in the latter category: The Denver sandwich. The concept was basic enough: It’s a Denver omelet – you know, an omelet studded with diced ham, onions and green peppers – cooked and enfolded in two slices of toasted bread.

Apparently it’s a rarity, given Lonely Planet’s description of the beast:

6. Denver (aka Western)
Range: Highly endangered. Native to Denver but has not been seen in the wild for some time.
Which came first: the sandwich or the omelet? Given that the Denver sandwich is a Denver omelet in a roll, you would assume that the omelet predates the sandwich. Oddly, this doesn’t appear to be the case, with published references to Denver sandwiches predating the omelet by several years. The Denver omelet – the classic blend of ham, bell pepper, onions and egg – in evolutionary terms is a sandwich that lost its shell. The Denver sandwich is currently the ivory-billed woodpecker of the sandwich kingdom.

We did a bit of 21st-century poking around — aka googling — and came up with several recipes for this sandwich. As it turns out, it’s also known as the Toasted Western, the “Western” being another name for the Denver omelet, perhaps perpetrated by jealous types in points north. (Yes, we are talking about you, Wyoming.)

Still, after 15 years in Denver, we had never encountered this sandwich on a Mile High menu. And that includes classic breakfast places such as Sam’s No. 3, Pete’s Kitchen and Breakfast King.